In its infancy, mobile communication was based on an analog radio transmission referred to as Advanced Mobile Phone System (AMPS). AMPS provided adequate transmission for an emerging mobile communications consumer market; however, within a few years the emerging market grew to millions of subscribers that demanded more and more airtime, which pushed analog technology to the limit. As a result, dropped calls and busy signals became common, which fueled research and development for an improved mobile communications network.
In response, industry developed digital wireless technologies that could accommodate increased network traffic within a limited amount of radio spectrum. One such technology is Global System for Mobile (GSM), which employs Time Division Multiple Access (TDMA). TDMA comprises a time-sharing protocol that provides three to four times more capacity than AMPS. In general, TDMA employs a technique wherein a communication channel is divided into sequential time slices. A respective user of a channel is provided with a time slice for transmitting and receiving information in a round-robin manner. For example, at any given time “t,” a user is provided access to the channel for a short burst. Then, access switches to another user who is provided with a short burst of time for transmitting and receiving information. This cycle continues, and eventually each user is provided with multiple transmission and reception bursts.
Shortly after TDMA was introduced, Code Division Multiple Access (CDMA) was developed and represented an enhanced solution to analog transmission. Code Division Multiple Access provides “true” sharing, wherein one or more users can concurrently transmit and receive via employing spread spectrum digital modulation, wherein a user's stream of bits is encoded and spread across a very wide channel in a pseudo-random fashion. The receiver is designed to recognize and undo the randomization in order to collect the bits for a particular user in a coherent manner. Code Division Multiple Access provides approximately ten times the capacity of analog technologies and enables increased voice quality, broader coverage and increased security. Today, CDMA is the prevalent technology employed in mobile systems.
Technological advances paved the way for the mobile communications industry to improve GSM and CDMA technologies and develop new technologies. One such improvement includes EDGE (Enhanced Data-Rates for GSM Revolution) technology. The evolution of GSM to EDGE mitigates various issues associated with voice traffic bandwidth and provides higher data throughput, which increases efficiency and higher performance. For example, EDGE provides for data rates up to 384 Kbps (with a bit-rate up to 69.2 Kbps per timeslot) over broadband. In addition, EDGE provides for more robust services such a Short Message Service (SMS) and Multimedia Message Service (MMS) for messaging, XHTML (including WAP) browsing, Java applications, FM radio reception, video streaming, and voice and image recording technologies.
Recently, the International Telecommunications Union adopted an industry standard for third-generation (3G) wireless systems that can provide high-speed data rates (e.g., for data transmission and Internet use) and new features. Currently, three operating modes—CDMA2000, WCDMA and TD-SCDMA—based on CDMA are being developed. CDMA2000 technology provides a relatively simple, quick, and cost-effective path to 3G service. CDMA2000 1x technology supports voice and data services over a standard CDMA channel. Additionally, it provides up to twice the capacity (e.g., peak data rates up to 153 kbps and projected peak data rates up to 307 kbps, without compromising voice capacity) of early CDMA networks. The additional capacity accommodates growth in the Internet market. Moreover, CDMA2000 1x provides longer standby times and is backwards compatible. CDMA2000 1x EV-DO technology provides a data optimized version of CDMA2000 with peak data rates over 2 Mbps and an average throughput of over 700 kbps, which is comparable to DSL and can support video streaming and large file downloads. WCDMA and TD-SCDMA provide more complex enhancements.
As mobile communication transmission evolves, the electrical and software industries are concurrently developing mobile devices that are smaller, consume less power, cost less and include more applications. One obstacle confronted by mobile device designers is the need to provide isolators between filtering components and front/back ends. Such isolators can consume valuable space within already densely populated circuitry and increase design complexity.